1. Field of the Invention
The present invention relates to an electrostatic separation and classification apparatus for separating and classifying a mixture of powders and/or particles of resin, rubber and the like in accordance with material types.
2. Description of the Prior Art
This type of electrostatic separation and classification apparatus includes an apparatus which makes use of frictional electrification and electrostatic field. For instance, an apparatus shown in FIG. 7 comprises a pair of opposed electrodes 1, 2 disposed in predetermined spaced relation, a charged material-to-be-classified supply portion 3 disposed above spacing between the electrodes 1 and 2, and a collecting portion 4 disposed below spacing between the electrodes 1 and 2.
A high voltage is applied between the electrodes 1 and 2 to produce an electrostatic field therebetween. In this state, a mixture of powders and/or particles of previously charged resin, rubber and the like is supplied from the supply portion 3 into the electrostatic field.
The powders and/or particles of the mixture falling downward by gravity are attracted to the electrodes of their opposite polarities and drop while separated from each other in rightward and leftward directions and are then collected in the collecting portion 4 having partition walls 4a and 4b in such a manner as to be classified depending upon different fall positions.
Such an apparatus includes an apparatus of the type having vertically extending, parallel opposed flat electrodes which is disclosed by Kali and Salz Entsorgung in Germany. (See "Nikkei New Material", Nov. 16, 1992, pp. 32-33.)
Another apparatus shown in FIG. 8 comprises a drum 6 rotating in a predetermined direction and a rotary electrode 7 obliquely above and spaced apart from the drum 6. The apparatus of FIG. 8 is adapted such that a charged mixture is supplied from a charged material-to-be-classified supply portion 8 above the drum, and the mixture falling in the electrostatic field between the drum 6 and the rotary electrode 7 is separated and classified into attracted, repelled, and intermediate materials in accordance with differences in polarity of the charged powders and/or particles of the mixture.
In FIG. 8, the reference numerals 9 and 10 designate separating plates, 11 and 12 designate collecting containers, 13 designates a scratching piece, and 14 designates a guide element.
However, in the prior art structure of FIG. 7, fine powder of the mixture and dust attracted by static electricity adhere on surfaces of the electrodes I and 2 during continuous operation of the apparatus.
Such deposits, if left as they are, irregularly drop in lumps by vibration generated when the mixture particles strike the electrodes 1, 2 and mechanical vibration of an exterior feeder, and are mixed with the powders and/or particles classified in the collecting portion 4, which may result in deterioration of separation accuracy and charge accumulation that induces ignition.
Thus, it is necessary to stop operating the apparatus for maintenance which includes scratching off or knocking away the deposits adhering on the surfaces of the electrodes 1, 2 at regular and frequent intervals. This has caused a decreased rate of operation.
In the maintenance, an operator is required to scratch off or knock away the deposited fine powder and dust from the surfaces of the electrodes 1 and 2 and might touch the exposed electrodes in high-voltage or charge-accumulated positions, resulting in a strong likelihood of electric shock.
Similarly, the prior art structure of FIG. 8 is required to stop operating the apparatus when the deposits on the surface of the rotary electrode 7 are scratched off or knocked away. This results in a decreased rate of operation and a strong likelihood of electric shock during the maintenance in the event of a failure because of the exposed surface of the rotary electrode 7.